In this proposal we plan to test the hypothesis that progesterone-induced increments in LHRH levels in the estrogen-primed ovariectomized rats result from increased influx of excitatory signals which, in turn, activate the appearance of new LHRH in the median-eminence. Electrical stimulation of appropriate site(s) in the diencephalon of freely-moving rats and analysis of labelled precursor incorporation into LHRH by high performance liquid chromatography (HPLC) will be the major new methods of investigation. In another related project the site(s) of impairment--pre or post-adrenergic receptors--which may be responsible for blockade of the pre-ovulatory LH surge will be examined in progesterone-blocked ovariectomized rats and middle-aged spontaneous persistent estrous rats. The effects of naturally occurring neuroactive agents--neurotransmitters and prostaglandins--infused intermittently into the third ventricle of freely-moving rats and their effects on LH secretion will be analyzed. The application of these three new approaches will clarify our understanding of the action of progesterone on the brain.